The present invention relates to improvements in vapor recovery fuel dispensers, in particular improvements in retrieving vapors which have hitherto been oftentimes lost.
Vapor recovery dispensers have been known for a good many years, and have been required in California and other areas with high proportions of hydrocarbons in the atmosphere for a number of years. The vapors to be recovered are located initially in the automobile tank and are displaced by the incoming liquid fuel as the tank is being refueled. The most widely used systems have operated on the "balance" principle in which an outer sheath is provided at the nozzle to fit around a filler pipe of an automobile gasoline tank. The sheath, if all goes right, makes a tight fit around the filler cap so that the vapor can pass only through the sheath (or, as it is commonly called, the "boot"), to a vapor return line connected with the service station's fuel tank. Thus, as the fuel is taken from the station's fuel tank and pumped into the automobile, the liquid volume being reduced is supplanted with returning vapors.
However, the balance systems, with their boots, are very cumbersome, at best, and oftentimes do not make a good fit with the automobile tank filler pipe, so that vapors are lost to the atmosphere.
Recently, Gilbarco, Inc. of Greensboro, N.C. has promoted a vapor recovery system that it markets as VAPOR VAC#. This is a bootless system, with the vapors being returned under positive drive by a vapor pump located in the vapor return line, as disclosed in U.S. Pat. No. 5,040,577 to Pope and assigned to Gilbarco, Inc. Various improvements on the Pope apparatus disclosure are made in U.S. patent Appln. Ser. No. 07/946,741 of Edward A. Payne entitled "Vapor Recovery Improvements" filed Sep. 16, 1992. Both of these disclosures are hereby incorporated herein by reference.
One of the advantages accruing from the use of a separately-provided vapor pump in the vapor return line is the ability to precisely control the vapor flow through the vapor return line, so that the vapor flow rate can be tailored to prescribed conditions. This is outlined more in the Payne application referred to above.
However, in the implementation of virtually all vapor recovery systems, except those which have perfectly formed boot seals, some vapor is invariably lost to the atmosphere, forming pollution. Applicants have found that one of the major vapor losses occurs at the start of the fueling process, as the liquid fuel is first released from the nozzle into the fuel filler pipe. This "puff" of vapor is released quickly, as a transient event. The vapor recovery pump is effective in drawing virtually all of the vapor liberated, once the transient event has passed. It is not desirable to raise the vapor pumping rate on a continuous basis, since air will be drawn in, which might lead to a dangerously lean vapor condition or over pressure in the storage tanks. Accordingly, means is still needed to deal with the transient event of the "puff" loss, which occurs at the start of liquid fueling.